Parasites are a real health issue when it comes to koi fish. The most common way koi fish contact parasites is from other fish but also from frogs and birds dropping and any other little creatures that visit the pond. Before a new koi is introduced to the pond, it is  important that the new fish be quarantined for at least 2 weeks. During this time period the koi should be treated for parasites. Isolating a koi in a quarantine tank, without treating the koi, is no assurance that the koi is parasite free. All that tells you is that if it has parasites, there are not enough of them to make it sick at this time. If you do not have a separate quarantine tank in which to treat a new koi in, then be very careful who you purchase your new koi from. Make sure the dealer is very conscientious about treating all their koi to make sure they are parasite free before they sell them.

The  most common parasites that affect koi fish are: Flukes, Costia, Chilodinella, Trichodina, Ich, Internal Parasites, Anchor Worm, and Fish Lice. All of these parasites are microscopic which means you cannot see them without the aid of a microscope with the exception of Anchor Worm and Fish Lice. 

The most common signs that you may have parasites are:

* Fish are flashing. Flashing is when a fish swims slowly near the side or bottom of the pond and then quickly swims off by first rubbing it's side against the pond wall or bottom.
* A fish is isolating itself from the other fish.
*One or more fish have stopped eating.
* A fish spends much of the time near the water fall gasping for air.
* Fish are sitting on the bottom of the pond with their fins clamped close to their body or are drifting in the pond with their head pointed upward or downward for several minutes at a time.
*Sores developing on the fishes body or fins.
* Fish are dying.

When selecting a treatment to rid koi of a particular parasite, you should always try to select a treatment that will effectively kill the parasite, while at the same time, cause the least amount of stress to the koi. An infestation of parasites can be very stressful to a koi. For this reason, it is very important when treating a koi with parasites to select a treatment that will not stress them anymore than is necessary. Proper treatment for parasites depends on which parasite the koi have. If you have access to a microscope, by simply taking a scraping from the fish and examining it under the microscope, you can usually tell exactly which parasites are present and then treat for them accordingly. Make it a habit to deworm any new fish coming into your pond.
*Medicine Section for treatment